GENERAL INFORMATION
The IPS is designed to allow full icing operations by automatically deicing
MR blades and anti-icing TR blades. The functioning of the system
is controlled automatically (with two independent Channels A and
B) in relation to the severity of the icing conditions encountered at any
time. An additional cockpit indicating panel shows the status of the IPS
and additional IPS Master Warning and Caution lights (Figure 3) are
provided for both pilot and co-pilot positions.
Main Rotor Ice Protection is provided by electrical heating of the MR
blades (sequential heating of six leading edge zones along the blade
span). Tail Rotor Ice Protection is provided by continuous heating of
the leading edge of the four blades.
Electrical power is provided by two Main Gearbox mounted AC generators.
Electrical power to the blades is controlled by a control box and
distributed through distribution boxes and slip rings. Atmospheric
information is provided to the control box by Outside Air Temperature
Sensors and Ice Detectors sensors (Liquid Water Content - LWC). The
Ice Detectors and windshield heating are active at all times with the
IPS ON.
The MR de-icing system works in AUTO by allowing a small amount of
ice to accrete on each leading edge zone and then sequential heating
of each zone causes the ice to be shed. It is normal, therefore, to see
an increase in torque required that will cycle up and down in accordance
with the heating cycles. Part of the torque increase (2 3%) is
due to the power required by the AC generators which also supply the
TR anti-ice function when the IPS is set to AUTO mode.
The torque variation, due to ice, can be expected to be around 5 χ
15%, depending on OAT, LWC, and Water Droplet size (Mean Volumetric
Diameter - MVD) when the system is working in icing conditions.
Higher torque increase may be experienced in more severe
icing conditions (higher LWC, larger MVD), but such conditions do not
occur frequently in the atmosphere.
No rotor unbalance is to be expected as a consequence of ice shed,
because of the symmetric 5 MR blades heating and the continuous TR
blades heating.
Ice shedding from the MR will be experienced during system functioning
in ice and this can occasionally be seen and heard, with small
pieces of ice striking the windscreens.
With the IPS selected ON and in AUTO mode on the overhead panel
(See Figure 1), an encounter with ice is indicated by the ICING caution
illumination on the MFD CAS, when OAT is less than +4°C and LWC
values being shown on the IPS Panel ICE SEVERITY window (See
Figure 2). Icing is also indicated by a build up of ice on visible aircraft
structure, e.g. unheated area of windscreens, wiper arms, SLD
marker.
The SLD marker is a composite sphere, installed on the right side of
the fuselage, in view of the pilot through the lateral screen. It is
designed to help the pilot visually detect if SLD conditions are encountered.
The sphere has a black central circle with yellow and red rings
around it. Ice accretion can be easily seen on the black marker.
A MANUAL mode is provided, selectable by the pilot, that overrides
the normal control system and applies the maximum possible heating
to the MR blades.
Different types of ice will form on the aircraft depending on the icing
conditions. The main types of ice are Glaze and Rime. Glaze ice is
clear and will tend to form at higher sub-zero temperatures (0°C to -
5°C) and is more likely with higher LWC and larger droplets. This type
of ice can generate high drag increase to occur due to the shape that
forms. Rime ice is white and opaque and tends to form at lower temperatures
with smaller droplets. Rime ice forms in a more streamlined
shape and causes a smaller increase in aircraft drag. It is possible to
have a mixture of both, which is know as Glime or Mixed Ice.
Flight in Freezing Rain or Freezing Drizzle is not permitted because it
is not covered by the current Airworthiness Rules for any type of aircraft.
Freezing Rain and Drizzle (also known as Supercooled Large
Droplets - SLD) consists of supercooled water droplets of sizes
greater than the EASA/FAA CS/Part 29 Appendix C, atmospheric definition
used for Certification. These conditions, although rare, have a
serious effect on any aircrafts performance. Pilots must use normal
operational planning and techniques to avoid flight in these conditions.
If encountered inadvertently, the conditions must be vacated immediately.
PILOT ACTIONS IN CASE OF SEVERE ICE ENCOUNTERS
Severe icing conditions are indicated by some or all of the following:
High PI rise (>30% above normal for flight condition)
Steady increase in base PI with heating cycles
High LWC (>1.5 g/m3)
Heavy amounts of water streaming across windscreens
Evidence of SLD (ice forming on sides of aircraft, SLD
Marker)
Increase in vibration
Tendency for significant speed loss.
Actions:
Reduce speed to 80 KIAS
Select 102% NR
Use up to 110% PI
Check for system failures
Select MAN
if PI reduces Select AUTO, and use MANUAL to
reduce subsequent PI rise.
if PI does not reduce, or rises steadily, select AUTO
and do not select MAN again (possible runback ice)
Change altitude severe ice conditions are usually near the
top of the clouds
Consider vacating icing conditions if severity does not reduce
Just a copy&paste from the supplement
Regards
Aser